Happy Nights Adrift On The Moon’s Sea Of Showers

Over 700 miles across, Mare Imbrium (Sea of Rains) is the largest lunar sea. Its roughly circular shape is defined by a series of mountains ranges just coming into good view tonight and the next few nights. Credit: Joseph Brimacombe

If you’re looking for a great little place to point a small telescope the next few nights, let me suggest Mare Imbrium, the largest of the lunar “seas”. That’s Latin for Sea of Showers or Sea or Rains. Lovely name. The last time it rained there was never.

Wide view of the whole Moon with the Imbrium basin circled. While Imbrium is the largest lava-filled “sea”, the largest basin, the South Pole-Aitkin Basin, is 1,600 miles in diameter. Credit: Silvercat/Wikipedia

All the Moon’s seas are enormous basins excavated by asteroid impacts between 3.1 and 4.2 billion years ago. Cracks and fissures in the Moon’s crust from the collisions served as conduits for deeper lava to rise and fill the basins with molten rock. These great pools cooled and solidified, forming the large grey spots that make up the face of the Man in the Moon that even a child notices today.

Ruptures in the Moon’s crust caused by the impact of large meteorites/asteroids creates what astronomers call multi-ringed basins. They look like bulleyes, a fitting comparison under the circumstances. Credit: Steven Dutch

Many of the seas are ringed by mountain ranges formed by faulting of the lunar crust during the impacts aided by slumping of material off the fresh slopes.

Earth’s mountains in contrast are lifted up when tectonic plates collide or pile up during volcanic eruptions.

Three ranges shape the outer boundary of the Sea of Rains – the Carpathians, the majestic Apennines and Caucasus. The Alps form part of a second inner ring of peaks. Each is named for its sibling range in Europe. Over the next few nights we’ll see all four cast awesome shadows as the Sun rises over their craggy peaks.

This is how our featured region of the Moon will appear tonight from the Americas. Mountain ranges are labeled in black, craters in white. Credit: Virtual Moon Atlas / Patrick Chevalley and Christian Legrande

Tonight features the Alps, Apennines and Caucasus and the spectacular craters Plato and Copernicus. Tomorrow night, the Carpathians, north of Copernicus, come into view. The reason these features look most dramatic now rather than closer to full Moon is because the terminator cuts across the region. Along the terminator, the boundary separating lunar day from night, the Sun is just rising and every little peak casts a shadow.